title: Segregation of the pathways leading to cortical reaction and cell cycle activation in the rat egg.
abstract: At fertilization of the mammalian egg, resumption of the cell cycle and the cortical reaction are two events of egg activation, correlated with an increase in intracellular Ca2+ concentration and activation of protein kinase C. To evaluate the pathways leading to both events, rat eggs were parthenogenetically activated by the calcium ionophore ionomycin, or by the protein kinase C activators 12-O-tetradecanoyl phorbol-13-acetate (TPA) or 1-oleoyl-2-acetylglycerol (OAG). Cortical granule exudate was visualized by the lectin Lens culinaris and Texas Red streptavidin, using a confocal microscope. Resumption of meiosis was detected by Hoechst dye, and intracellular Ca2+ concentration by fura-2. Ionomycin triggered both a cortical reaction and resumption of meiosis, while chelation of intracellular Ca2+ rise by BAPTA-AM (1,2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester) revealed a segregation between these two events. A low Ca2+ transient (approximately 150 nM) induced a partial cortical reaction in half of the eggs, but the meiotic status was not affected. TPA triggered a cortical reaction with neither resumption of meiosis nor intracellular Ca2+ rise, while OAG induced both aspects of activation, as well as a significant intracellular Ca2+ rise. We conclude that in the cascade of events leading to egg activation, the initial Ca2+ rise is followed by a segregation in the pathway. A relatively low Ca2+ rise is sufficient to induce a partial cortical reaction. However, a higher level of Ca2+ is required to complete the cortical reaction and resumption of meiosis. The activation of the cell cycle is Ca2+-dependent, but protein kinase C-independent.
authors.affiliation: Department of Embryology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
authors.forename: T
authors.initials: T
authors.lastname: Raz
authors.forename: D
authors.initials: D
authors.lastname: Ben-Yosef
authors.forename: R
authors.initials: R
authors.lastname: Shalgi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D037102:Lectins; D008540:Meiosis; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D037121:Plant Lectins; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014966:Xanthenes
chemical_list: D002614:Chelating Agents; D004075:Diglycerides; D007476:Ionophores; D037102:Lectins; D037121:Plant Lectins; D014966:Xanthenes; C033619:lentil lectin; D004533:Egtazic Acid; D015759:Ionomycin; C034657:Texas red; C038237:1-oleoyl-2-acetylglycerol; D011493:Protein Kinase C; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium